Thermal degradation of zinc polymethacrylate and a zinc methacrylate/methyl methacrylate copolymer

Methyl methacrylate and zinc methacrylate have each been polymerised in methanol solution using azodiisobutyronitrile as initiator and a copolymer of the two monomers has been prepared in the same medium.The degradation behaviour of the three materials has been studied using TG and TVA, volatile products have been investigated by infra-red and GLC analysis and infra-red spectroscopic examination of structural changes in the partially degraded polymer has been carried out for zinc polymethacrylate (ZnPMA).The breakdown of ZnPMA shows many similarities to the behaviour of the alkaline earth polymethacrylates. The effect of introducing ZnMA units into the PMMA chain by copolymerisation is to stabilise the chain considerably and to modify the degradation behaviour of the MMA units, so that methanol and carbon monoxide, resulting from side group scission, become major products in addition to MMA monomer; the ZnMA units in the copolymer behave in the same way as in ZnPMA.This study provides support for the mechanism previously proposed for the degradation of PMMA/ZnBr₂ blends, in which the ZnMA/MMA copolymer structure was regarded as an intermediate stage in the reaction.